1. Technical Field
The present invention relates in general to the masking of devices during processing and, in particular, to an improved system and method for improved masking of sensors during processing for better sensor edge control and track width definition for sensors having a narrow track width.
2. Description of the Related Art
Current mask processes can be prone to track width (TW) control and junction definition issues between the various layers of the product that define the sensor width. Some of these problems are illustrated in FIG. 1, which is a tunneling electron microscope (TEM) image of a sectioned masked wafer site 17. For example, the freelayer has a TW length 11 that is wider than the width 13 of the mask. In addition, the side 15 of the mask (e.g., into and out of the page) is relatively rough rather than straight, and the edges of the diamond-like carbon (DLC) mask layer are sloped rather than relatively sharp.
The reasons for these variations are the different reactive ion etching (RIE) etch rates for the different mask layers. For example, duramide etches significantly faster (e.g., about 45 Å/sec compared to about 16.7 Å/sec) than either DLC or photoresist (e.g., TIS). Since duramide is the masking layer for DLC, there is no static mask for DLC. This makes it nearly impossible to obtain well-defined DLC edges, which can induce large junction variations.
FIG. 2 depicts one prior art example that illustrates the results of these differences in etch rates. The left side of FIG. 2 depicts an initial spin step 21 wherein layers of photoresist (e.g., TIS) 23, hydronhilic polymers of acrylamide (e.g., DURAMIDE) 25, and DLC 27 are formed on a sensor 35. In step 29 (center of FIG. 2), the layers are exposed and developed such that photoresist 23 is reduced, while DURAMIDE 25 and DLC 27 are essentially unchanged. In RIE/ion mill step 31 (right side of FIG. 2), the various layers are reduced, but it is virtually impossible to predict or control the resultant width 33 of the layers. Although these conventional processing techniques can produce desirable results, the inability to consistently manipulate the end results is less than satisfactory. In particular, it would be helpful to obtain a well-defined carbon mask that does not depend upon the fast-etched DURAMIDE layer for TW definition.